I'm about out of options-loss of power - Page 2 - PeachParts Mercedes-Benz Forum

muleears · #16 07-26-2007, 11:50 AM

Could a plugged cat contribute to harder starting? The last month or so this car has been taking a few more revs. than it used to to start. Could there be a connection?

Brian Carlton · #17 07-26-2007, 11:56 AM

Quote:

Originally Posted by muleears

Could a plugged cat contribute to harder starting? The last month or so this car has been taking a few more revs. than it used to to start. Could there be a connection?

I've heard such tales, but, I don't buy it.

If the cat was so plugged that it affected airflow on crank, the engine would barely idle........if at all. The crank speed would be less than the usual speed if such a situation were to occur.

captainmonk · #18 07-26-2007, 12:10 PM

seems to me any engine with that many miles restricted airflow would certainly make it concievable the ole gurl needs another revolution or 2 to get up to speed But what would i know I only have 409000 on mine
I think a sawzall to the cat will elimanate the problem

ConnClark · #19 07-26-2007, 12:52 PM

I don't think its the cat. You say your 0 to 15mph acceleration seems normal and this will rule that out. You have a one of the following, a boost leak some place, a waste gate thats stuck wide open, an ARV is stuck open, a massive exhaust leak before the turbo, or a bad turbo.

As far as keeping the cat clean, nothing is going to work until you get your smoke problem taken care of. There are two things your needs to stay clean, Heat and Oxygen. With excess fuel your not going to get the oxygen.

This is what I do to keep the cat clean. Drive up a long steep hill with your foot to the floor to raise the EGTs. When you get to the top of the hill pull your foot out of it then down shift. You want the engine to turn above 4000 rpm briefly with no fuel. This sudden surge of fresh air hits the hot cat and helps burn it clean. You might get a puff of black soot out the back as you down shift. This is good as you are blowing some of the soot out. I always try to do this at the beginning of a long trip as the sooner you do it the more fuel you save. Also the extended highway speeds keep EGTs high and help burn out the rest of the crud in the cat.

Jim Wickham · #20 07-26-2007, 02:35 PM

BS

I just went through this with my 87... did all the same stuff as you did and to no avail..

IT'S POINTING TO PLUGGED CAT... mine did it and this is what you do to test...

1. hope you have forgiving neighbors.

2. put front of car on jack stands in garage.

3. take the three nuts off the flange holding downpipe to turbo.

4. take the four bolts out of the flanges connecting the front section of exhaust to the rear section (this will be mid-way back on the car)

5. take the two bolts/bushings out of the brace still holding the pipe just before the cat (cat is flat wide part of that first section of exhaust pipe)

6. get a large pipe wrench about 16-18 inches long and put it on that down pipe up near the turbo and you'll generally need to apply a good amount of force to twist it just a little, then it should fall off.

7. put the car back down on all 4s and give her a test run... I'd be willing to bet she has a mint more pickup/pulling power.

8. if number 7 is the case Gut the cat TOTALLY including steel wool stuff and replace the pipe under the car.

muleears · #21 07-26-2007, 05:18 PM

I pulled the bolt out of the exhaust mani as Wolfsburg suggested, didn't get a great deal of carbon/soot out. The casual acceleration is better but the 0-60 isn't. What does this mean?

Brian Carlton · #22 07-26-2007, 05:29 PM

Quote:

Originally Posted by muleears

I pulled the bolt out of the exhaust mani as Wolfsburg suggested, didn't get a great deal of carbon/soot out. The casual acceleration is better but the 0-60 isn't. What does this mean?

It means nothing because the volume of exhaust that can pass through the opening provided by the removed bolt is probably 1% of the total exhaust volume at maximum available power.

muleears · #23 07-26-2007, 05:59 PM

After having driven it a little more, the difference with the bolt out is marginal at best. So I guess I need to remove the cat somehow to check it?

Brian Carlton · #24 07-26-2007, 07:31 PM

Quote:

Originally Posted by muleears

After having driven it a little more, the difference with the bolt out is marginal at best. So I guess I need to remove the cat somehow to check it?

Just disconnect the downpipe from the manifold and support it somehow with wire. It'll make some noise but they'll be no restriction from the cat if that's the problem.

muleears · #25 07-31-2007, 07:14 AM

Haven't been able to disconnect the exhaust to check the cat yet but I did remove the ALDA, all it did was make it smoke more. The ARV and EGR are disabled. I'll be buying the fittings today (hopefully) to attach my pressure guage to the nipple on the IM. I'll report back with boost numbers as soon as I can. If I've got boost and plenty of fuel doesn't that mean it MUST be the cat?

The change in performance was rather sudden. Over the course of a weekend it went from running great to poor. Now the performance varies. Leaving one stoplight I think I could walk faster. At the next light it is sometimes better. First and second gear are fair, once it hits third its a dog. If I slow from 60 or so down to 30, acceleration from there is really poor. It won't downshift without the kickdown. All that pedal and no acceleration makes lots of smoke

While under the car this weekend I noticed a torn boot on a rear axle, I guess I send it to my indy and let him fix the boot and take a look at the cat.

One final thought, about this same time I had an instance where it wouldn't shift into fourth without some coaxing. When I got home I checked the fluid and it was a pint low. Refilled and all was fine. Two days later same thing happened. It has been 10 days since then and has needed no more fluid. I can't remember if the performance problem and the tranny problem happened at the same time but they were within a day or two of each other. Could the tranny have a problem that won't let the car accelerate? I know I have to give it a lot more pedal than I used to to gain any speed. Under light acceleration it seems to shift normally, when pushed hard it struggles to shift into the next gear. Doesn't slip, it just stays at the high RPM a second or two too long then "lunges" into the next gear. Mobil 1 and filter done about 10K ago.

Sorry for the lengthy post but I know there is a lot of knowledge here and I want you all to have all the info possible to help me solve this problem.

Thanks again,

muleears · #26 07-31-2007, 04:37 PM

After finding the fittings to attach my pressure gauge, I drove the car and got no boost at all. When I removed the hose from the gauge I heard a pssst sound. I thought "what the heck" I attached my mityvac and found 6 inches of VACUUM at 4K RPM

What is going on

I attached the line to the nipple, with the circle around it, on the IM shown in the attached pic.

How can I have vacuum at 4000RPM's

Somebody please tell me how stupid I am and what to do!

Bad turbo? Stuck wastegate?

Magoo · #27 07-31-2007, 09:04 PM

It's gotta be either the turbo or wastegate, like you said.
Lack of function in either case makes it a normally aspirated engine = vacuum in intake manifold.

Brian Carlton · #28 07-31-2007, 09:12 PM

Quote:

Originally Posted by muleears

After finding the fittings to attach my pressure gauge, I drove the car and got no boost at all. When I removed the hose from the gauge I heard a pssst sound. I thought "what the heck" I attached my mityvac and found 6 inches of VACUUM at 4K RPM

What is going on

I attached the line to the nipple, with the circle around it, on the IM shown in the attached pic.

How can I have vacuum at 4000RPM's

Somebody please tell me how stupid I am and what to do!

Bad turbo? Stuck wastegate?

If you have vacuum at 4000 rpm's, there is a serious intake restriction. The engine is desperately trying to get more air and cannot do so.

The wastegate has nothing to do with this.

First thing to check is the air cleaner. Any obstruction on the intake side..........leaves.........a rag..........anything?

Then, check the turbo. See if it rotates freely. If it's jammed for any reason, the engine cannot get sufficient air.

It's a fairly simple solution now that you've got the data. Just find it.

muleears · #29 08-01-2007, 07:46 AM

Brian and Magoo,
Thanks for the advice. I checked the intake last night, clean as a whistle (new filter also), I guess that leaves the turbo. Found a couple on ebay for $2-300 or would I be better off at a pick a part? Can it be rebuilt?

Brian Carlton · #30 08-01-2007, 11:19 AM

Quote:

Originally Posted by muleears

Brian and Magoo,
Thanks for the advice. I checked the intake last night, clean as a whistle (new filter also), I guess that leaves the turbo. Found a couple on ebay for $2-300 or would I be better off at a pick a part? Can it be rebuilt?

Did you try and rotate the turbo with your fingers to see if it's free to turn?

The problem cannot be the turbo unless the impeller/turbine combination has frozen in place and won't allow airflow. If it rotates, then it's not the culprit, IMHO. The turbo may not provide boost for a variety of reasons, but, it cannot cause vacuum unless it fails to turn and blocks the intake airflow.